1. Field of the Invention
This invention relates to a process for preparing aminoalkylsilanes by contacting chloroalkylsilanes with ammonia or a lower alkylamine under pressure at an elevated temperature. More especially, this invention relates to the preparation of aminoalkylalkoxysilanes by reaction of chloroalkylalkoxysilanes with ammonia or a lower alkylamine under elevated temperature and pressure. More especially, this invention relates to an improved manipulative technique for effecting the reaction whereby production of impurities is minimized and the desired product is obtained in a greater volume-time yield.
2. Discussion of the Prior Art
Broadly, it is known to prepare aminoalkylsilanes by reaction of chloroalkylsilanes and ammonia and at an elevated temperature and pressure. Such is described, for instance, in U.S. Pat. No. 2,832,754. According to the process therein disclosed, which is useful for the preparation of aminoalkylalkoxysilanes, reactants are together placed in a pressure vessel which is then closed and heated to a temperature of at least 90.degree. C. According to the disclosure of the aforenoted Patent, the reaction necessarily producing bis-(alkoxysilyalkyl)-amines of the general formula EQU HN[(CH.sub.2).sub.n -Si(R').sub.x (OR).sub.3-x ].sub.2
and tris-(alkoxysilylalkyl)-amines of the formula EQU N[(CH.sub.2).sub.n -Si(R').sub.x (OR).sub.3-x ].sub.3
where n=1 to 3, x=0, 1 or 2, R' is methyl and R is alkyl of 1 to 3 carbon atoms (as by-products). The formation of these secondary and tertiary amines is explainable by the fact that a portion of the chloroalkylalkoxysilane reactant reacts with formed primary amine resulting in production of these bis and tris by-products.
According to the patent, formation of these by-products can be minimized by using a great excess of ammonia. However, even with a twenty-fold molar excess of ammonia, the yields of primary amines, i.e., desired products such as .gamma.-aminopropyltriethoxysilane, are only around 50%.
It is therefore a problem of providing .omega.-aminoalkylsilanes, especially .omega.-aminoalkylalkoxysilanes by reaction of the corresponding chloroalkylsilanes and ammonia or lower alkylamines without the formation of substantial quantities of secondary and tertiary amines. It is an object of this invention, therefore, to provide a process whereby such aminoalkylsilanes and aminoalkylalkoxysilanes can be provided at high volume-time yields by reaction of the corresponding chloroalkylsilanes and ammonia or a lower alkylamine. It is a further object of this invention, therefore, to provide such a process whereby the yields of primary aminoalkylsilanes are increased with concomitant decrease in the yields of secondary and tertiary amines. It is still a further object of this invention to provide such a process which can be carried out at more moderately elevated temperatures than required according to the Patent aforenoted.